Various types of current image diagnosis apparatuses can obtain three-dimensional image data (to be referred to as volume data hereinafter) as well as a two-dimensional image of one slice. There have been proposed various display methods which allow users to easily analyze obtained volume data.
Methods of displaying volume data which are generally and frequently used include, for example, a method of displaying three arbitrary slices (to be referred to as MPR (MultiPlanar Reconstruction) images hereinafter) perpendicular to each other and a method of displaying a projected image from a given line-of-sight direction by volume rendering (to be referred to as VR hereinafter). The user can freely observe a region that he/she wants to view, from a desired direction, by changing the positions of these arbitrary slices or changing the line-of-sight direction on a volume rendering image (to be referred to as a VR image hereinafter).
When observing a VR image in this manner, the user sometimes loses sight of a point or region on which he/she has focused his/her attention (to be referred to as a target region hereinafter) while rotating the displayed image or changing a region displayed on a VR image. With regard to this point, marking a target region on a VR image will facilitate analysis on volume data. A VR image is a two-dimensional image, where a target object with depth information is projected on one screen. For this reason, unlike setting an ROI (Region Of Interest to be referred to as a 2D-ROI hereinafter) in a two-dimensional slice (two-dimensional image), simply setting a 2D-ROI on a VR image will not determine its position in volume data. That is, it is not possible to uniquely designate a target region.
When setting a three-dimensional region of interest (to be referred to as a 3D-ROI hereinafter) in volume data, the user conventionally uses a method of designating a corresponding region in an arbitrary slice. When, for example, designating a measurement region at the time of volume measurement, the apparatus displays an arbitrary slice image including a target stereoscopic region. The user then designates several points on the displayed slice image to create a closed curve. The user rotates the volume data relative to a predetermined axis in a slice including the created closed curve. The user designates points on another slice based on the rotated volume data by a method similar to the above operation. Repeating such a series of operations can specify the region designated by the user in the end. In addition, since closed curves are created on a plurality of MPR images, it is possible to create a 3D-ROI with a relatively complex shape. In addition, in order to reduce the load on the user, it is possible to designate one point on an arbitrary slice and create a 3D-ROI in a spherical shape including a predetermined radius, instead of a complex shape, in volume data.
Setting a 3D-ROI in the volume data allows the user to freely observe a desired region from a desired direction without losing sight of it.